Folding devices, such as boards or plates, have long been used to longitudinally fold webs and other sheet-like materials in order to form a stack of folded sheets. The sheets are, generally speaking, drawn over the folding device wherein the shape and configuration of the device causes the sheet to twist and bend thereby producing the desired fold. Folding devices have heretofore been provided in a variety of shapes and configurations in order to achieve the desired fold lines and folding patterns. Folding devices have been used to form a number of different folds including, for example, half-folds, quarter folds, c-folds, v-folds, j-folds, w-folds, z-folds, and so forth.
In addition, for more complex folds requiring multiple fold lines, it is known to form the necessary fold lines using two or more folding devices in series. In this regard, folding boards have also been used in series to achieve inter-folded or inter-leafed sheets, that is to say sheets folded such that they partially envelope portions of another sheet. Inter-leafed sheets are commonly employed in stacks as a mechanism to facilitate removal of the individual sheets from a dispenser. Withdrawal of a first sheet through a dispenser opening pulls the enveloped potion of a second sheet through the dispenser opening such that it extends out of the dispenser opening and is exposed. Having a portion of the subsequent sheet extending out of the dispenser opening greatly facilitates removal of the same from the dispenser by the user. By way of example only, various folding devices, folding patterns and inter-folding schemes are described in the following U.S. Pat. Nos. 3,401,928; 3,679,094; 3,817,514; 3,841,620; 4,131,271; 4,502,675; 5,868,276; 6,045,002; and 6,168,848.
These folding devices are often advantageous since they allow folding of rolls of sheet material and, typically, allow for increased converting speed relative to many mechanized or rotary folding machines. However, due to the manner in which the sheets are folded, stress and friction associated with drawing the continuous sheet material across and/or through the folding devices can cause various aesthetic and physical defects within the sheet material. As an example, the twisting and pulling forces can alter the dimensions of the sheet material. In addition, these and other physical forces can also create undesirable wrinkles or creases in the sheet material. In this regard it is believed that the stress resulting from the twisting forces and friction cause the sheet material to xe2x80x9cbucklexe2x80x9d or wrinkle in order to decrease the physical forces upon the sheet. Further, when using multiple folding devices in a series, these same forces can act to degrade previously formed fold lines and/or to cause prior folds to xe2x80x9crollxe2x80x9d thereby changing the location of the fold within the sheet material. This can, undesirably, cause the formation of a fold line with an irregular orientation, i.e. a fold line that does not have uniform direction and/or placement. Still further, these forces can also cause the formation of a double fold line, i.e. a xe2x80x9cshadowxe2x80x9d fold. These and like irregularities are defects that are aesthetically displeasing to the end user. Further, defects such as irregular fold lines and other fold defects can also create problems with packaging and/or dispensing of the product. For example, stacks of folded sheets are commonly packaged in a clip and variation in stack height, such as due to variations in sheet folds, can make packaging difficult or ultimately destroy the packaging clip, such as where a paper sleeve is used.
Thus, there exists a need for folding devices capable of longitudinally folding webs and sheet materials that avoid the formation of defects such as wrinkles and unwanted creases. Further, there exists a need for such a device that produces uniform fold lines and prevents the formation of irregularly oriented fold lines. Still further, there exists a need for a folding device that avoids the formation of double folds along an intended fold line. Still further, there exists a need for a folding device that generates accurate and stable dimensions within the resulting folded product and stack.